a)Author to whom correspondence should be addressed; current address: School of Earth and Environmental Sciences, Seoul National University, San 56–1 Silllim-dong, Gwanak-gu, Seoul 151–747, Korea; electronic mail: hjung@ucr.edu

Abstract

One of the major goals in the experimental study of deep earthquakes is to identify slip instabilities at high pressure and high temperature (HPHT) that might be responsible for the occurrence of earthquakes.Detectingacoustic emissions from a specimen during faulting provides unique constraints on the instability process. There are few experimental studies reporting acoustic emissions under HPHT conditions, due to technical challenges. And those studies have used only one or at most two acoustic sensors during the experiments. Such techniques preclude the accurate location of the acoustic emission source region and thus the ability to distinguish real signal from noise that may be coming from outside the sample. We have developed a system for detectingacoustic emissions at HPHT. Here we present a four-channel acoustic emissiondetecting system working in the HPHT octahedral multianvil apparatus. Each channel has high resolution (12 bits) and a sampling rate of 30 MHz. In experiments at the pressures up to 6 GPa and temperatures up to 770 °C, we have observed acoustic emissions under various conditions. Analyzing these signals, we are able to show that this system permits us to distinguish between signal and noise, locate the source of the acoustic emission, and obtain reliable data on the radiation pattern. This system has greatly improved our ability to study faulting instabilities under high pressure and high temperature.

Received 15 June 2005Accepted 03 November 2005Published online 12 January 2006

Acknowledgments:

The authors thank Wenjie Jiao, Chris Hididiacos, Liqiang Liu, and Jin Ma for providing detailed technical information in designing the acoustic emission system. The authors also thank Baosheng Li for providing information on his interferometry and piezoelectric transducers. David Georges helped the authors to set up some of the hardware. One of the authors (H.J.) thanks G. Gudfinnsson and S. Keshav for useful discussions. We also thank Frank Forgit for sample assembly preparation. This project was supported by the NSF Grant Nos. EAR-0125938, EAR-0135411 (H.W.G.), EAR-0125097 (Y.F.), and the Carnegie Institution of Washington.